Conversion of mannose to fructose

Abstract

An economical method of converting mannose to fructose uses a mannose isomerase from Pseudomonas cepacia immobilized on an alumina containing polyethyleneimine crosslinked with an excess of glutaraldehyde. The method utilizes mannose-containing aqueous solutions as the feedstock, and affords solutions in which at least 55% of the mannose has been converted to fructose. Because of the relatively higher levels of fructose than can be obtained by isomerizing glucose to fructose using glucose isomerase, substantial savings in separation of high fructose-containing products can be achieved. The process described represents the first economical mannose isomerase process.

What is claimed is: 
     
       1. A method for producing fructose comprising enzymatic isomerization of mannose in an mannose-containing aqueous feedstock comprising a delignited hemicellulose hyrolysate with a mannose isomerase immobilized on a support, said isomerization conducted at a temperature from about 30° to about 60° C. and a pH from about 5 to about 8.5 for a time sufficient to convert at least 55% of the mannose to fructose, and recovering the isomerized product mixture, where said mannose isomerase has the characteristics of the mannose isomerase produced by pseudomonas cepacia and said support comprises a refractory inorganic oxide selected from the group consisting of alumina, silica, thoria, magnesia, titania, and combinations thereof, impregnated with a polyamine selected from the group consisting of ethylenediamine, diethylenetriamine, triethylenetetraamine, tetraethylenepentaamine, pentaethylenehexaamine, and polyethyleneimines, said polyamine being crosslinked with an excess of a bifunctional reagent selected from the group consisting of phthalaldehyde, toluene diisocyanate, and X(CH 2 ) p  X, where p is an integer from 2 to about 8 and X=--CN or --CHO, so as to provide a multiplicity of pendant functional groups. 
     
     
       2. The method of claim 1 where the aqueous mannose-containing feedstock comprises an aqueous solution of purified mannose. 
     
     
       3. The method of claim 1 where the mannose isomerase is immobilized on a support of alumina impregnated with a polyethyleneimine crosslinked with an excess of glutaraldehyde so as to afford a multiplicity of pendant aldehyde groups. 
     
     
       4. The method of claim 1 where the isomerization is performed at a temperature between about 35° to about 45° C. 
     
     
       5. The method of claim 1 where the isomerization is conducted at a pH between about 7 and about 7.5. 
     
     
       6. The method of claim 1 where the isomerization is conducted for a time sufficient to convert at least 60% of the mannose to fructose. 
     
     
       7. The method of claim 1 where the isomerization is conducted for a time sufficient to convert at least 65% of the mannose to fructose.